The long-term goal of our research is a deeper understanding of interrelationships between the central nervous system and the glands of internal secretion, especially brain-pituitary interactions and the pituitary-gonad axis. Comprehension of the nature, extent, sites and mechanisms of action of gonadal and pituitary hormonal feedback influences on neuroendocrine function remains a major objective. This applies not to the stimulating and inhibiting effects of gonadal steroids on pituitary-gonad function and reproductive behavior in the adult but also to the organizing action of the steroids on sexual differentiation of the brain in the embryo or neonate and the changing thresholds at puberty. Rhinencephalic and other extrahypothalamic regions of the brain are being explored as well as the isolated hypophysiotrophic area ("hypothalamic island"). The control of secretion of ovarian progestins and their specific actions on the brain and the pituitary gland are questions of continued interest. Methods of inducing and overcoming sterility are being actively investigated. A continued systematic attack on these neuroendocrine relationships is proposed, employing the techniques of neuroanatomy, neurophysiology, pharmacology and endocrinology.